1. Field of the Invention
This invention relates in general to the field of powder metallurgy and in particular to an improved and less expensive method and apparatus for generating controllable pressure pulses (both in the shock regime and in a rapid, but shock-free, regime in the same device) for the purpose of consolidating (compacting) powders to a contiguous rigid form, primarily for the purpose of producing material samples and manufactured parts. In this field, the emphasis is generally on producing higher quality and better performing parts, which generally means parts with higher density, strength and ductility, and doing so at lower cost.
2. Description of Related Art
Powder metallurgy (P/M) offers possibilities for the design of materials into near net shape which exhibit a wide range of unique and novel properties. In principle, there is no limitation on the production of a material with any desired composition by such methods. However, the high cost of powder metallurgy technology must compete with other low cost manufacturing methods.
Below, we first describe two specific market areas (soft and hard magnetic materials) of some commercial interest as an example of the need. Other markets for other materials are of equal interest. The dynamic compaction of conventional powders using the described invention as a low cost high tonnage compact press is expected to have high value in the part manufacturing industry. Then we describe present powder consolidation technology and dynamic powder consolidation techniques and their limitations.
Soft Magnetic Materials
The world-wide magnetic materials market is a multi-billion dollar industry, and soft magnetic materials comprise a significant fraction of this market. Soft magnetic materials play a key role in a number of applications, especially with respect to electric power applications. Some of these applications include electric motors, distribution transformers, and generators.
Soft magnetic materials find applications in electrical, electronics, and computer systems that characterize modern society. Soft magnetic materials play a key role in power distribution, make possible the conversion between electrical and mechanical energy, underlie microwave communication, and provide both the transducers and the active storage material for data storage in information systems. As the properties of these materials are continuously being improved, many new applications are likely to emerge.
The critical properties necessary in designing optimum soft magnetic materials include a high saturation magnetization, low coercivity, low hysteresis loss, high permeability, low magnetostriction, low eddy current losses, high Curie temperature, low temperature dependence of the magnetic properties, and cost. In practice, the available materials must compromise some of these properties in favor of others. For example, permalloys (Fe—Ni-based alloys) have a tremendously high permeability and very low coercivity, but the saturation magnetization is only approximately 60 percent of the value for α-Fe.
Many of the requisite properties are intrinsic, such as a high saturation magnetization and magnetostriction. These properties are tailored through the specific design of the alloy. Other properties are influenced by extrinsic factors, most notably by microstructural features. The magnetic properties strongly influenced by the microstructure are those involving domain wall motion. For example, the eddy current losses arise because soft magnetic materials generally operate in alternating fields. The losses arise primarily because of difficulties in reversing the magnetization state of the material. This, in turn, is controlled by domain wall motion; if domain wall motion is inhibited, the losses are greater. Microstructural features such as precipitates and localized strain fields from dislocations and impurity atoms provide pinning sites for domain walls. The eddy current losses also increase as the size of the magnetic regions increases and as the resistivity decreases. Thus, the eddy current losses can be reduced by reducing the coercivity and the scale of the microstructure and by decreasing the electrical resistivity.
The coercivity is affected by both intrinsic and extrinsic factors. Intrinsically, the coercivity is controlled by the specific anisotropy of the crystal lattice (magnetocrystalline anisotropy). While cubic crystals possess the lowest anisotropy, there is variability between different cubic materials. For example, the anisotropy constant (the parameter that describes the degree of anisotropy) differs by almost an order of magnitude between Fe and Ni. As with other intrinsic properties, the anisotropy can be altered through alloy design.
The primary extrinsic influence on the coercivity is the microstructure. The microstructure, in fact, influences the entire shape of the hysteresis loop. Some examples of microstructural features that influence the coercivity by affecting domain wall motion include defect density, including dislocations and point defects (e.g., impurity atoms). Therefore, it is critical to control microstructural features in order to produce more efficient soft magnetic materials.
One microstructural feature that greatly impacts the coercivity is the structural correlation length (D). In crystalline materials, the structural correlation length is equal to the grain size, while in amorphous materials it is essentially the distances over which short range order exists. As grain sizes decrease from the millimeter size range to approximately 0.1 μm, there is a corresponding increase in coercivity proportional to 1/D. However, when the structural correlation length approaches the ferromagnetic exchange length, which is on the order of the domain wall width, the coercivity begins to decrease. With a continuing decrease in the structural correlation length, the coercivity was observed to decrease with a D6 dependence. This dramatic decrease in coercivity has been attributed to the averaging of local anisotropies by the exchange interactions, with the net effect of eliminating (or significantly reducing) the influence of magnetocrystalline anisotropy on the magnetization process.
The strong dependence of coercivity on the structural correlation length has prompted a significant amount of research in the areas of nanocrystalline and amorphous alloys, where D ranges from 0.5 to 50 nm. Amorphous alloys typically consist of Fe— or Co-based alloys with additions of Si and B, which enhance the glass formability, and other alloying additions to control, for example, the magnetostriction. Currently, nanocrystalline microstructures are formed by the crystallization of specific amorphous alloys, with the resulting microstructure consisting of 10 to 15 nm crystallites surrounded by an amorphous matrix. The primary advantage of amorphous and nanocrystalline alloys is the reduction of the anisotropy and, in the case of nanocrystalline materials, magnetostriction. Amorphous metals have been used in place of grain-oriented Si steels in transformer applications, which provided a reduction of 75 percent in eddy current losses because of reduced coercivity and magnetostriction. However, the saturation magnetization is significantly reduced, with values ranging from 10 to 15 kG for current amorphous and nanocrystalline alloys (compared to 21.5 kG for α-Fe). The lower saturation values result from the dilution of the Fe or Co alloys with elements that enhance glass formability or alter other intrinsic properties. Future advances in soft magnetic materials will be made by increasing the saturation magnetization while retaining the advantageous properties of amorphous and nanocrystalline microstructures.
Generally, nanocrystalline and amorphous materials are produced in particulate form by atomization or melt spinning techniques. Practically, the consolidation of nanocrystalline and amorphous particulate into useful engineering devices provides many unique challenges. Most densification techniques rely on elevated temperatures to promote densification. However, exposure to elevated temperatures significantly degrades the hard-won microstructural features through crystallization and grain growth. Other techniques utilize binders, allowing low temperature consolidation. Using binders, however, dilutes the amount of magnetic material in the final part to, at most, 70 percent by volume, resulting in a lower saturation magnetization by volume in the final engineering component.
Dynamic consolidation techniques allow densification to full density without prolonged exposures to elevated temperatures and the concomitant degradation of the microstructures. Dynamic consolidation techniques utilize shock waves of sufficient strength to generate interparticle welding and melting, with temperature excursions essentially eliminated. Shock waves generated by, for example, explosives or projectiles have been utilized to densify rapidly solidified particulate materials in a wide variety of alloy systems, including magnetic materials. Most dynamic consolidation techniques, however, are not amenable for large-scale production techniques. Novel techniques to generate sufficient shock waves must be developed in order to fully realize the benefits of dynamic consolidation on a practical level.
Dynamic consolidation techniques are desirable to consolidate soft magnetic nanocrystalline and amorphous materials. Dynamic consolidation will allow full densification without deleterious effects on the microstructure. Thus, the benefits of nanocrystalline and amorphous microstructures on the magnetic properties can be retained in the final engineering component.
Hard Magnetic Materials
Permanent magnet materials significantly affect a wide spectrum of industries, with applications in such diverse areas as microelectronics, the automobile industry, medical devices, and power generation. Applications in permanent magnet motors alone require some 920 tons of fully dense and 770 tons of bonded Nd—Fe—B magnets annually. Currently, the permanent magnet industry is a $4.05 billion industry, with projections reaching $10 billion for 2005.
Hard magnetic materials find applications in the automotive, aerospace, and telecommunication industries. For their size and weight rare earth magnets, such as NdFeB, have a higher energy density than other hard magnets. These magnets are used in compact powerful electric motors for computer disk drives and fly-by-wire aircraft. They also find applications as high precision actuators used to focus the laser in a compact disk player and in miniature loud-speakers of personal stereos. Automotive applications include starters, small motors, alternators, sensors, meters, and electric and hybrid vehicle propulsion systems. These magnets are made from powdered metal by forming to shape under pressure and sintered.
Two materials comprise almost 90 percent of the hard magnetic market: ferrites (58 percent) and Nd—Fe—B (31 percent). With only modest magnetic properties, with a maximum energy product of approximately 5 MGOe, the principal advantage of ferrite is its inexpensiveness, especially in terms of raw materials cost. It is used in applications where size and weight are not design considerations. When magnetic strength is more paramount than cost, Nd—Fe—B magnets are favored. The energy product of isotropic Nd—Fe—B magnets range from 7-8 MGOe for bonded magnets to 15 MGOe for fully dense hot pressed magnets. The energy product of anisotropic Nd—Fe—B magnets range from 45 MGOe for commercially available products to 54.4 MGOe for magnets produced on a laboratory scale.
Requisite intrinsic properties necessary for high strength permanent magnets include a high saturation magnetization, large magnetocrystalline anisotropy, and a reasonably high Curie temperature. In addition, the properties of any real material are strongly influenced by extrinsic factors, most notably the microstructure. Such factors as the microstructural scale, phase content and grain morphology and orientation strongly influence a material's properties. These factors also greatly influence the magnetic properties, especially the scale of the microstructure. Superior properties arise when the grain size is below a critical limit known as the single domain limit. When the grain size is larger than the single domain limit, multiple domains are present in each grain. This multiple domain state leads to relatively easy demagnetization and poor hard magnetic properties. When the grain size is below the single domain limit, demagnetization is much more difficult, leading to excellent hard magnetic properties. The single domain limit is related to specific intrinsic magnetic properties, including the anisotropy constant and the saturation magnetization. For Nd—Fe—B magnets, the single domain limit is approximately 300 nm.
For isotropic permanent magnets, it is imperative that the grain size be below the single domain limit. Because of this requirement of a fine grain size, non-equilibrium processing techniques are required. Currently, the commercially preferred technique to generate a fine-scale microstructure is melt spinning. Depending on the processing parameters, melt spinning generates a microstructure that ranges from fine, equiaxed grains on the order of 20 to 30 nm to an amorphous structure that crystallizes during consolidation. It is critical to retain as fine a microstructure as possible upon further processing to optimize the magnetic properties.
Monolithic Nd—Fe—B permanent magnets useful in applications are produced by the consolidation of comminuted melt spun ribbon. Isotropic Nd—Fe—B permanent magnets, with energy products of approximately 12-15 MGOe, are consolidated by conventional hot pressing techniques. However, during the relatively prolonged times at elevated temperatures, grain growth occurs, resulting in deleterious effects on the magnetic properties. Anisotropic magnets are produced by die upset processing of the hot pressed magnets. Die upsetting results in crystallographic alignment through preferred grain growth. The high degree of crystallographic alignment results in higher energy products. However, the additional exposure to elevated temperatures during die upsetting further degrades the microstructure. The degradation in the microstructure and the limited crystallographic alignment achievable limits commercially available energy products to 45 MGOe, only 70 percent of the theoretical maximum of 64 MGOe.
On a laboratory scale, efforts have been made to retain the beneficial microstructural features produced during melt spinning. This has been accomplished through consolidation by shock and explosive compaction. These dynamic consolidation processes result in extremely short exposure to elevated temperatures, allowing the fine microstructures generated during melt spinning to be retained. The dynamically consolidated magnets retained the magnetic properties and microstructures of the initial melt spun ribbon. In addition, die upsetting of shock-consolidated amorphous ribbon resulted in an anisotropic fine-grained monoliths with an energy product of 54.4 MGOe (85 percent of the theoretical maximum).
The laboratory-scale tests illustrate the benefits of retaining a fine microstructure in the final consolidated magnet. However, scale-up of the previously mentioned dynamic consolidation techniques provide unique challenges. The development of other dynamic consolidation processes that limit the material's exposure to elevated temperatures while providing consolidation to near full density will provide a route to materials with improved magnetic properties. In addition, the development of processes that retain fine microstructures during consolidation would provide an avenue to commercially produce magnets utilizing novel magnetic materials that absolutely rely on a nanocrystalline microstructure, such as the recently discovered nanocomposite or spring-type magnets.
Non-magnetic Powders
The dynamic compaction of conventional powders (ferrous and non-ferrous) using the described invention as a low cost high tonnage compact press is expected to have high value in the part manufacturing industry because of higher green density and green strength in the resulting parts at faster compaction rates. According to the trade association, Metal Powder Industries Federation (MPIF), the P/M (powder metallurgy) parts and products industry in North America has estimated sales of over $2 billion. It is comprised of 150 companies that make conventional P/M parts and products from iron and copper-base powders; and about 50 companies that make specialty P/M products such as superalloys, tool steels, porous products, friction materials, strip for electronic applications, tungsten carbide cutting tools and wear parts, rapidly solidified powder products, and metal injection molding (MIM) parts and tool steels. P/M is international in scope with growing industries in all of the major industrialized countries. The value of U.S. metal powder shipments (includes paste and flake) was $1.9 billion in 1996. Annual worldwide metal powder production exceeds one million tons.
MPIF estimates the MIM North American market to exceed $100 M and to grow at an annual rate of 20 to 25%. There was an estimated 25 to 40 companies in North America manufacturing MIM products either as job shops or in plant departments. This growth rate is fueled by strong auto production and an increase in PM parts applications in auto engines and transmissions. The advanced particulate materials sector of the PM industry has a bright future, especially PM high speed tool steels, PM superalloys and composites, MIM and spray formed parts, materials, and fibers. PM parts and products made from advanced particulate materials will find new applications in automotive, aircraft engine, electronic packaging, computer peripheral equipment and medical markets. Looking ahead, PM nickel-based superalloys and advanced composites are being considered for the NASA high speed civilian transport plane. According to MPIF, the PM parts industry will outpace metalworking due to increases in applications for PM components, longer term growth of the industry will continue to gain metalworking market share, and the use of PM parts in industrial markets especially automotive is now widely recognized for contributing significantly to cost and performance competitiveness.
An example of advanced materials, is the intermetallic compound TiAl, possessing the ordered (γ-fct) structure, has attractive and unique properties for extended high temperature applications. Parts made of aluminides (TiAl, Ti3Al, NiAl, NbAl3, etc.) and other intermetallic compounds have potential for applications requiring light weight and high-temperature strength and oxidation resistance. Intermetallic compound powders made by rapid solidification processing (RSP) are brittle and hard, making it difficult to consolidate these powders by conventional techniques. The high temperature exposures for long times, involved in the conventional techniques, causes excessive grain growth and phase transformation of the initially RSP microstructure. Therefore, to ensure ductility and other desired mechanical properties these parts need to be formed by consolidation of the RSP powders. Also, room-temperature brittleness is a problem with conventional intermetallics. The challenge, then, is to develop powder consolidation techniques that do not adversely affect any enhancements due to RSP. Intermetallics are also used as matrices in composite materials. Here, the goal is consolidation without incurring excessive reactions between matrix and reinforcement.
Present Powder Consolidation Technology and its Limitations
Conventional Powder Consolidation Techniques
Several conventional consolidation techniques and their variants for particulate materials exist. These include die pressing, cold (CIP) or hot isostatic pressing (HIP), reactive sintering, powder injection molding, ceramic consolidation, and electroconsolidation which produce consolidated products.
Conventional powder compaction is performed by die pressing. The die provides the cavity into which the powder is pressed and gives lateral constraint to the powder. An external feed shoe vibrates the powder into the die. An upper and a lower punch are used for most compaction. Both punches are loaded to generate stress within the powder to produce the part. There are several modes of pressing and thus several types of presses including hydraulic, mechanical, rotary, isostatic, anvil, etc. These are all very large, noisy, complex, and expensive systems. The limitations of conventional die pressing include limited green density, limited green strength, green density gradients, need for binders and binder removal (a slow and expensive process), and shrinkage of parts during sintering.
CIP is used for complex shapes involving undercuts or large length to diameter ratios. A flexible mold is filled with powder and pressurized isostatically using a fluid such as oil or water. CIP is typically performed at pressures below 350 MPa (megapascals) although pressures up to 1400 MPa have been achieved. While higher green densities with less density gradients are reached at a given pressure when compared to die pressing, most of the other limitations of die pressing exist in CIP.
In HIP, a gas-tight can is used to contain the powder. Volatile contaminants are removed by heating and vacuum degassing. The can is then sealed and pressed in an internally heated pressure vessel. Argon gas at high pressure is used to transfer heat and pressure isotropically to the compact, leading to densification. After HIP, the can is stripped from the densified compact. This is a low strain rate process because the stress rise is slow. The long time exposures at high temperatures lead to grain growth and loss of the initial fine and rapidly solidified microstructures.
Several variants of reactive sintering have been employed to consolidate metallic and intermetallic materials. The basis of all reactive sintering processes is the formation of a liquid phase as a result of an exothermic reaction between elemental powders present in the mixture. The liquid phase accelerates consolidation and is consumed during the process. The reaction may proceed with no pressure (reactive sintering), with isostatic pressure (reactive hot isostatic pressing, RHIP) or unidirectional pressure (reactive hot pressing, RHP). As an example, the typical process steps for NiAl-20 volume % TiB2 composite are as follows:                1) Ni and Al (along with TiB2) are mixed to stoichiometric proportions.        2) Compacts are pressed to a green density of approximately 70% of theoretical.        3) Compacts are vacuum encapsulated in 304 stainless steel.        4) Encapsulated compacts are pressed at 1200° C. and 172 MPa for 1 hour.        
A disadvantage with reactive sintering is the difficulties associated with HIP, which often accompanies or succeeds reactive processing, such as the need for ductile canning materials that do not react with the powders and the need to seal cans carefully. The expenses associated with welding HIP cans and expense of reactive metals such as Ti and Nb overcomes the low costs associated with reactive sintering step.
Powder injection molding involves extrusion of a mixture of powders, any reinforcements, and a binder through a die. The extrusion should be performed above the softening temperature of the binder. After extrusion the binder is removed (thermally or by wicking action) and the compact is consolidated to approximately full density by HIP. Fully dense Al2O3-reinforced composites of NiAl and MoSi2 have been produced successfully by this method. This process offers the possibility of producing complex P/M parts. However, the principal disadvantages are the difficulty of complete binder removal and the inability to produce continuous fiber-reinforced composites.
The Ceracon (for “CERAmic CONsolidation”) process uses a granular ceramic material as the pressure-transmitting medium (PTM) as opposed to the gas used in HIP. A preform of the material to be consolidated is preheated and immersed in the hot ceramic PTM. Pressures as high as 1.24 GPa (180×103 psi) are applied to the preform via the PTM for 30 to 60 seconds. The uniaxial pressure applied to the PTM bed is transmitted to the preform as quasi-isostatic pressure, and consolidation of the part takes place in 30 to 60 seconds. Both the Ceracon and HIP processes operate in the plastic-yielding range and it is possible with the Ceracon process to produce full densification almost exclusively by plastic yielding, which is essentially instantaneous. The high consolidation pressure available, in the Ceracon process, permits the temperature to which the material is exposed to be relatively low (compared with HIP and hot pressing) and the exposure times to be short. This allows full densification of the material while maintaining the fine microstructure. In composite materials interfacial reactions between the matrix and reinforcement phases are minimized or eliminated. Critical parameters of the process include part temperature, PTM temperature, applied pressure, strain rate, preheat time and temperature, and hold time at temperature.
The electroconsolidation process uses graphitic-carbon particles, having controlled electrical properties, as both the PTM and as an electrical resistor for simultaneous heating and consolidation of powder preforms in a modified hot-pressing facility. This technique is being evaluated for rapid pressure-assisted densification, to near-net shape, of metal and ceramic powder preforms, whisker-reinforced ceramic composites, and other materials that require, or could benefit from, pressure-assisted consolidation at very high temperatures. Electroconsolidation is a member of the family of “soft” tooling, pseudo-HIP, or containerless-HIP consolidation processes that use a particulate “pseudo-fluid” as the PTM. A cold preform is heated to the consolidation temperature by resistive heating of the surrounding medium, within the die, simultaneously with the application of the compaction pressure. This “inside-out” method of preform heating is particularly advantageous for densifying nonoxide ceramics and other materials that require very high temperatures for consolidation to near theoretical density. Such temperatures are difficult to achieve by other powder-vehicle compaction methods that require transfer of either a preheated preform or the heated medium into the compaction vessel. In development work, a 50-t (55 ton, 490 kN) and a 100-t (110 ton, 980 kN) presses were adapted for electroconsolidation.
Electroconsolidation was demonstrated to compact SiC preforms to near-theoretical density. The cold compacted preforms were oven dried, baked, and then heat treated at 1500° C.
Electroconsolidation followed, using a compaction pressure of 28 MPa (4000 psi) and a nitrogen atmosphere. At power levels above 20 kW rapid densification was obtained; densities of 90+% and 95% of theoretical were obtained in less than 2 minutes and 4 minutes respectively. Parts were rapidly heated by the conductive medium to about 2000° C. (3630° F.). Advantages of the process, compared with conventional hot pressing and HIP, include: rapid cycle times (minutes versus hours), high temperature capability (to 3000° C., 5430° F.), controlled atmosphere capability (inert or active gases), and the ability to densify complex shapes without “canning”. Because densification is rapid, this process has the potential for inhibiting grain growth, resulting in fine-grain parts having the improved mechanical properties associated with this fine microstructure. In addition, high-vacuum or high-pressure pumps are not needed, and the ability to adapt existing hot-pressing systems can help keep equipment costs down.
Materials Modification, Inc., (MMI) has developed and patented a powder consolidation technique called Plasma Pressure Compaction (U.S. Pat. Nos. 6,187,087; 6,183,690; 6,001,304; 5,989,487). This is based on the plasma activated sintering (PAS) technique published by several investigators. In the PAS process, densification is achieved by a combination of resistance heating with pressure application and plasma generation among the powder particles. The time for high temperature and pressure application is short, of the order of minutes rather than hours, to reach full densification. Difficult to sinter materials such as covalent ceramics, oxygen sensitive intermetallic compounds, and superconductors have been consolidated by PAS. MMI's Plasma Pressure Compaction technique claims to consolidate submicron and nanomaterials (metals, intermetallics, and quasiceramics) at reduced consolidation time, lower oxygen content in the final part, higher density (tungsten to 97% and rhenium to 96% dense), and reduced processing temperature.
Dynamic Powder Consolidation Techniques
In addition to the above conventional techniques and their variants, there are dynamic consolidation techniques which use explosives, impact, and pulsed magnetic forces to yield full densities. Dynamic (shock) consolidation and synthesis of materials have been used to a considerable degree in research activity on materials development. Shock-wave consolidation of powders was used for the first time in the 1950's to produce high density parts from materials used in aerospace and atomic energy applications. Dynamic consolidation has the potential to meet the challenges to consolidation of advanced materials such as intermetallic monolithic and composite materials, and become a cost effective technique for fabrication of intermetallic-based parts.
Conventional powder-consolidation methods, such as sintering and HIP, typically involve long times at high temperatures, and rely on solid-state diffusion. Dynamic consolidation typically involves high-pressure shock waves that travel at several kilometers per second through the sample. These shock waves are generated in the sample by various methods including detonating explosives to accelerate a “flyer plate” into the powder sample or using a gun to fire a projectile into the sample. Larger samples generally can be produced with explosives, while use of a projectile generally allows better control and measurement of experimental parameters such as impact velocity. Processing is generally achieved by discharge of a single high-energy pulse through a pressurized powder blend. Applied pressures range from 210 to 420 MPa and the specific energy inputs varied between 3200 and 4800 kJ/kg. Consolidation occurs by diffusion through a thin layer of liquid that is temporarily created between particles. As the shock wave passes through the powder, it gives up most of its energy at particle boundaries, possibly because of interparticle friction. Partial melting occurs near these boundaries, and the liquid rapidly solidifies by heat conduction into the relatively cool particle interiors. Dynamic consolidation can therefore be considered a “cold” method. Details of the actual consolidation mechanism depend on the powder and processing conditions. For example, solid-state bonding of particles sometimes occurs without partial melting, and melting may be caused by adiabatic heating generated by plastic deformation of particles, rather than by interparticle friction. Scientists at Rockwell International have dynamically consolidated rapidly solidified γ-Ti-48Al powder using explosive-launched stainless steel flyer plates. This dynamic consolidation resulted in a nonequilibrium single-phase alpha-2 (DO19) structure. When the same powder is hot pressed, the equilibrium lamellar mixture of 85 to 90 volume % γ and 10 to 15 volume % α-2 phases result. Rockwell scientists also dynamically consolidated SiC/Ti—Al—Nb composites resulting in a uniform dispersion of the SiC fibers in the aluminide matrix with a safe and very thin (50 nm) fiber/matrix reaction zone. The same composite when hot pressed resulted in a thick (more than 1 micrometer) fiber/matrix reaction zone that is deleterious to the fracture properties of the composite.
Potential advantages of dynamic consolidation, as identified by previous investigators, include:                Nonequilibrium microstructures produced in rapidly solidified powders can be retained in the compact. Consolidation occurs so rapidly that there is not enough time to re-establish equilibrium.        For the same reason above, composite materials can be fabricated with very thin reaction zones between matrix and reinforcement. This minimizes the formation of brittle reaction products that can degrade composite fracture properties.        Many powders that are extremely difficult or impossible to form by other methods can be dynamically consolidated. For example, some powders are so brittle that conventional isostatic pressing may cause excessive particle fractures.        Dynamic consolidation has the potential for fabricating net-shape parts.        Although most samples produced to date have been small (centimeter size), the process can, in principle, be scaled up to produce large (meter size) compacts.        
Even though dynamic consolidation can offer significant inherent advantages and versatility in forming both metallic- and intermetallic-based monolithic and composite materials, it is important to recognize that the method is still very much in the development stage, and major problems need to be addressed. For example, methods of precisely controlling process parameters and obtaining uniform samples must be developed. Cracking is another problem that must be solved. When the powder-consolidating shock wave reaches a free surface, it transforms into a relief wave that can fracture the sample. Also, the rarity of kinetic energy storage machines and the small sizes of samples produced to date make it difficult to predict whether kinetic energy discharge is a commercially viable way to consolidate powders.
The techniques discussed above are in various stages of R&D and prototype development.
Other alternative approaches for dynamic consolidation of powders are being pursued. For example, dynamic magnetic compaction (DMC) described in U.S. Pat. Nos. 5,405,574 and 5,611,139 is a process which claims to consolidate powders into full density parts in less than a millisecond. In this process, high currents are passed through a compactor coil, at the center of which is a powder container. The current in the coil generates a magnetic field, which in turn applies magnetic pressure up to 1400 MPa (200 ksi) to the powder (300 MPa is typically achieved), in two orthogonal directions. The pressure consolidates powders such as high-strength steels, titanium-nickel intermetallics, tungsten alloys, and superconductor ceramics. The process claims to consolidate powders at room or elevated temperatures in any controlled atmosphere, and claims that the forces can be controlled with precision. So far, the process has been used to compact small sized shapes (rods and bars 2 to 20 cm long and up to 2 cm thick); although it is claimed that there is no fundamental size limitation. One limitation of DMC is the general need for post sintering, under a reducing atmosphere such as hydrogen, or HIP to complete grain bonding. At the DMC pressures typically achievable (300 MPa) grain bonding is generally not complete. Note that the quoted peak pressure of 1400 MPa apparently leads to damage to the coil, and a consequently limited lifetime. Making survivable coils which can operate repetitively at pressures above 5-6 kbar is difficult.
All known techniques, both static and dynamic, are in general not cost effective compared to conventional wrought processing techniques and none of the dynamic techniques have generated any significant commercial activity. Therefore, cost effective consolidation techniques are needed which can produce near theoretical densities (i.e. nearly 100%), can enable sintering at lower temperatures to obtain preferred microstructures, and can allow fabrication of conventional die presses of small size and lower expense.